The invention relates to devices which are associated with turnstiles in order to permit their angular movements in a particular direction whilst instantaneously preventing their returns or angular movements in the reverse direction from the preceding one.
It relates more particularly, among these devices, to those which are arranged so as to exert as desired their instantaneous angular blocking role in one direction or the other and which comprise for this purpose:
a drum of revolution of axis X fast to the turnstile and coaxial with the latter,
a fixed vee whose bisector plane contains the axis X of the drum, this vee being open on the side of this drum and positioned at a short distance from the latter,
a roller of axis parallel with the axis X, interposed between the vee and the drum and mounted so that, on a moveable support, it can be moved between a first end position for which it is blocked by wedging between the drum and one side of the vee and a second end position for which it is blocked by wedging between the drum and the other side of the vee,
and electromagnetic means to urge the support as desired towards one or other of its two end positions corresponding to the end positions of the roller.
Such a dual-action angular anti-return device operates in the following manner.
When the roller is placed in either one of its two end wedging positions by suitable energization of the electromagnetic means, it is not possible to make the drum, and hence the turnstile, rotate in the direction which would tend to increase this wedging of the roller through the effect of friction which exists between this roller and the drum.
On the contrary rotations of the drum and of the turnstile in the reverse direction are possible at least when authorization thereof is given by control means known to the technician and outside the present invention.
When the electromagnetic means are not energized, the roller is found to be in an unwedged neutral position and angular movements of the turnstile are possible in both directions, provided that the abovementioned authorization has been given.
Dual-action angular anti-return devices of the above type have been described in U.S. Pat. of Applicant No. 4658940 and in general give every satisfaction.
However it may happen that certain difficulties will be encountered to suppress the angular blocking of the turnstile produced for a given direction in the manner indicated above: in certain cases, this suppression is not ensured automatically by simply annulling the energization of the electromagnetic means which have caused said blocking.
Now such automatic suppression is obligatory in certain installations, for example, to render possible an emergency evacuation under circumstances manifested by cutting off the general electrical supply of the anti-return device concerned.
In such circumstances, special means must be provided to temporarily and automatically urge the support of the roller in reverse direction from the preceding one.